Pituitary adenomas and hyperprolactinemia have been recognized in a substantial number of women. The possible relationship to estrogen exposure and oral contraceptive use is a matter of intense current interest. Estrogens are thought to increase prolactin secretion and pituitary growth, at least in part, by a direct pituitary effect. These effects are likely to be mediated by initial attachment to cytoplasmic receptors. The relationship between estrogens and the pituitary will be examined as follows: 1) Study if human pituitary prolactin secreting adenomas contain estrogen, progestin and androgen receptors. (Correlate to dopamine receptor). Compare the adenomas to normal human anterior pituitary. 2) Investigate properties of human prolactin secreting pituitary adenomas in culture. Study estrogen, anti-estrogen, and bromocriptine effects on prolactin secretion and cell growth. Attempt to develop permanent lines. 3) Study pituitary tumorigenesis in response to estrogens in mice. Contrast pituitary estrogen receptor systems and chronic estrogen responses in mouse strains that do (C57) and do not (C3H) develop pituitary tumors with chronic estrogen administration. Study the pituitary effects both in situ and in grafts to normal hosts. Investigate the effects of the anti-estrogen tamoxifen on tumor development and growth. 4) Investigate the use of a high energy emitting radioactive iodinated estradiol derivatve for selective pituitary (and adenoma) imaging in the living animal. These studies may increase our understanding of the mechanism of estrogen involvement in the development and the growth of human prolactin secreting adenomas and provide leads for potential prevention, diagnosis or treatment.